Forecasters now expect the storm to stay below hurricane force until it's in the Gulf of Mexico, staying to the west of Tampa, Florida, where the Republican National Convention starts on Monday, though there is still an outside chance it could hit there.

Forecaster Eric Blake of the U.S. National Hurricane Center said it is "too early to know" the storm's exact course, though projections indicated the storm could make U.S. landfall near the Alabama-Mississippi border.

In Haiti, the government and international aid groups announced plans to evacuate several thousand people from one of the settlement camps that sprang up in the aftermath of the 2010 earthquake.

Isaac was expected to dump eight to 12 inches (20 to 30 centimeters) of rain on the island of Hispaniola that is shared by Haiti and the Dominican Republic.

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"That kind of rain is going to cause some life-threatening flash floods and mudslides," said Dennis Feltgen, a spokesman for the Hurricane Center in Miami.

Isaac was centered about 165 miles (265 kilometers) south-southwest of Santo Domingo, the Dominican capital, on Friday morning, and its maximum sustained winds had increased to 60 mph (95 kph). It was moving west at 14 mph (22 kph), according to the Hurricane Center.

In flood-prone Haiti, where the storm's eye is likely to blow ashore late Friday, Prime Minister Laurent Lamothe urged people to avoid crossing rivers, to tape their windows, and to stay calm, saying "panic creates more problems."

Lamothe and other Haitian officials said the government had set aside about $50,000 in emergency funds and had buses and 32 boats on standby for evacuations.

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But among many Haitians, the notion of disaster preparedness in a country where most people get by on about $2 a day was met with a shrug.

"We don't have houses that can bear a hurricane," said Jeanette Lauredan, who lives in a tent camp in the crowded Delmas district of Port-au-Prince.

About 400,000 people remain in settlement camps comprised of shacks and tarps in the wake of Haiti's devastating 2010 earthquake.

In the Haitian capital of Port-au-Prince, people went to work as usual, but commercial banks were scheduled to close at noon and some residents took precautions as the sky darkened.

"Just in case this gets very bad -- the sky is turning gray -- I'm making sure we have enough food in the house," said 25-year-old Joanne Dorville as she carried home rice, sardines, black beans and cooking oil she had purchased in a street market.

Haitian authorities and aid workers from the International Organization for Migration and the Haitian Red Cross sought to evacuate as many as 8,000 people, some of them elderly and handicapped, from a tent camp at the edge of the capital, but few accepted Friday morning.

"If I leave for a shelter, by the time I come back, everything I have will be gone," said Charles Delizaire, a 39-year-old resident of the settlement named Marassa.

So far, Isaac itself had caused no reported injuries or deaths, but police in Puerto Rico said a 75-year-old woman died near the capital of San Juan on Wednesday when she fell off a balcony while filling a drum with water in preparation for the storm.

In the Dominican Republic, authorities began to evacuate people from low-lying areas but, as in Haiti, they encountered resistance.

"Nobody wants to leave their homes for fear they'll get robbed," said Francisco Mateo, community leader of the impoverished La Cienaga neighborhood in Santo Domingo, the capital.

Blake, the U.S. forecaster, said that while Isaac hadn't strengthened much in the Caribbean, it could gain power as it moves away from Cuba. "When it moves back over water, it has a chance to restrengthen," he said.

Commercial airlines, including American Airlines, canceled flights to and from the Dominican Republic, Haiti and Puerto Rico.

Organizers of next week's Republican National Convention in Tampa said they were working closely with state and federal authorities on monitoring storm as they prepared for the arrival of 70,000 delegates, journalists and protesters, and Florida Gov. Rick Scott said there were no plans to cancel the convention.

Out in the eastern Atlantic, another tropical storm, Joyce, was downgraded to a tropical depression late Thursday, and posed no threat to land. The hurricane center in Miami said Joyce had maximum sustained winds of 35 mph (55 kph) and that it was becoming disorganized.